The present invention relates generally to material fabrication, and more specifically to generating a tightly focused beam of large material particles as are useful for additive fabrication techniques.
Aerodynamic focusing of large particles is a technology which can be applied to various direct fabrication technologies, including direct laser fabrication (LENS), hot spray, and cold spray processing. The LENS process uses a laser to melt a small puddle on a working surface. Growth material in the form of large ( greater than 10 xcexcm) particles is then added to the puddle, some of which melts therein and becomes incorporated into the component being grown. In cold spray processing, rapid deposition of a wide range of materials occurs when large particles are delivered against a growth surface at velocities in the 400-1000 m/sec regime. Hot spray processing passes the particles through a laser, which melts the particles before the hit the growth surface. All of the above processes are capable of providing special material properties to the final component.
A primary difficulty which appears in all known direct fabrication technologies is to direct the material being added to the precise point where it is needed, thereby obtaining a finely detailed product. Unfortunately, current methods of supplying powders to the growth surface produce broad and unfocused patterns of powder distribution, whereas the desired distribution is narrow (e.g.,  less than 1 mm), and focused to a specific region.
The most common approach toward obtaining a spray of particles is to pass a carrier gas in which a series of particles is entrained through a simple expansion nozzle. The result is a wide and diverging plume of relatively slow particles. This plume can be narrowed by removing the outer regions of the plume with a particle diverter (e.g., a cone-shaped aperture with a hole at the apex), but this approach reduces the flux of particles to the extent that a fabrication process based thereon is impracticably slow.
There is therefore a need for a source of beams of large solid particles with velocity vectors accurately directed, or focused, along a single direction. Useful patterns of particles can be line-like (one-dimensional) or plane-like (two-dimensional) in the direction of motion.
The present invention is a device to generate tightly focused beams of large (1 xcexcm less than  less than L less than  less than 100 xcexcm) material particles. These particles can be generated in quantity, and with velocities ranging from a few feet per second to supersonic velocities with appropriate post-focusing acceleration. Such particle beams are of considerable importance for additive fabrication techniques, where the particles are directed precisely against the spot on a workpiece where they are to be added, whereupon an energetic influence (laser heating, heating due to impact deformation, etc.) causes the particle to merge with the structure of the workpiece. A single line-like beam source can deliver on the order of a cubic centimeter of particles per minute to a growing component, a value considerably in excess of those characteristic of present direct additive fabrication techniques with the further benefit of minimal overspray resulting in much higher efficiency in material usage.